1. Field of the Invention
This invention relates to an exhaust system, particularly for two-stroke cycle internal combustion engines, in which at least that portion which adjoins the internal combustion engine consists of two joined shell sections made of sheet metal and contains a catalytic converter.
2. Description of the Prior Art
Such exhaust systems have the advantage that their manufacture is rather simple and inexpensive. In exhaust systems comprising a catalytic converter for decreasing the emission of polluants in the exhaust gases it is difficult to ensure that the catalytic converter will be lighted off quickly, e.g., in case of a cold start, and that the catalytic converter will have a long service life even in case of a prolonged operation of the engine under full load although in such an operation the catalytic converter will be heated to high temperatures, which may damage the catalytic converter if the elevated temperatures are maintained for a long time.
It is already known to provide a main catalytic converter, which is preceded by a preliminary catalytic converter, which should be disposed as close as possible to the cylinder of the internal combustion engine so that the high temperatures occurring adjacent to the cylinder will cause the preliminary catalytic converter to be lighted off quickly and the main catalyst can then be installed in the exhaust system in a downstream part thereof, which is less important from the aspect of gas dynamics. In known exhaust systems the preliminary catalyst is designed to extend substantially throughout the cross-section of the exhaust system adjacent to said preliminary catalyst although that arrangement has the disadvantage that the dynamics will adversely be affected to a high degree so that the output power of the engine will be reduced.